A safety device for elevators may also be referred to as a “safety arrester”, which is an indispensable component of an elevator to guarantee safe operation of the elevator. With increasing requirements on safety and reliability of the elevator, requirements on deceleration or braking performance of the safety device for elevators are also increased.
The safety device for elevators is generally provided with a wedge, and in a normal operation of a common elevator, the wedge and a guide rail of the elevator are not in contact (there is a gap distance between the two), and in a deceleration or braking process, the arrestment similar to braking is caused by a frictional force between the wedge and the guide rail of the elevator, where the magnitude of the frictional force reflects the magnitude of an arresting force exerted on the guide rail. For example, when the elevator is in an abnormal state such as fast dropping, a speed limiter disposed in the elevator is used to judge whether a current dropping speed exceeds a predetermined speed value; if the current dropping speed exceeds the predetermined speed value, the speed limiter triggers an action, and further triggers a pulling transmission component of the elevator to act on the wedge of the safety device for elevators, so that a frictional force is generated between the wedge and the guide rail. The frictional force further pulls the wedge to move upward; therefore, the frictional force is increased rapidly, the wedge clamps the guide rail in a self-locking manner, and an elevator car stops moving, thus guaranteeing operation safety of the elevator.
When classification is carried out according to wedge structures, safety devices for elevators can be classified as symmetric arresters and asymmetric arresters. The U.S. Pat. No. 481,965, which is entitled “Arrester Device for Elevators” and belongs to the prior art, discloses an asymmetric arrester device, including an active wedge and a counter wedge that are asymmetrically disposed on both sides of a guide rail. In a deceleration or braking process, a downward acting force is exerted on the counter wedge through an elastic force of multiple disc springs disposed above the counter wedge, thereby obtaining a desired stable frictional force (that is, an arresting force) that can arrest an elevator car. However, such an asymmetric arrester device has at least the following disadvantages: (1) the force value repeatability of the elastic force generated by the multiple disc springs is poor, and therefore, the working stability of the safety device is easily affected; (2) a force value of the elastic force that can be exerted by the multiple disc springs depends on the number of disc springs superposed, and due to restrictions such as space, the force value of the elastic force that can be generated by the disc springs is usually limited, and a braking effect on a high-speed elevator may be undesirable; (3) due to an excessively high stiffness and an excessively small deformation amount, the disc springs are extremely sensitive to wear of the wedge; as the wear of the wedge changes, the elastic force that is generated by the disc springs when the active wedge moves upward to a predetermined position decreases significantly, the desired frictional force (that is, the arresting force) is hard to achieve, and therefore, there exists a potential safety hazard.